Technical Abstract:
Listeria monocytogenes is a food borne pathogen associated with severe disease in humans. We determined the prevalence, levels, antimicrobial susceptibility, and pulsotypes of L. monocytogenes in foodstuffs of common sale in three retail markets of Culiacan, Sinaloa, Mexico. The pathogen was isolated from 26 of 240 (10.8%) food samples. Raw chicken breasts showed the highest occurrence of contamination (23.3%, 14/60) followed by turkey frankfurters (11.7%, 7/60) and ground beef (8.3%, 5/60). L. monocytogenes was not detected in 60 soft cheese samples (25 g each). L. monocytogenes counts in food samples varied between 0.23 to 110 MPN/g. Twenty-three of the tested strains were resistant to a least one antimicrobial and were delineated into 16 antimicrobial profiles. More strains were resistant to ceftazidime and nalidixic acid than any of the other antimicrobials tested. The 26 strains (single isolate from each positive sample) were divided into eight distinct ApaI pulsotypes. PFGE revealed a low genetic diversity among the isolates, irrespective of the type of food or market from which the food was purchased, suggesting that select clonal types of L. monocytogenes clones are widespread. The occurrence of L. monocytogenes in these products reflects the need for periodic bacteriological controls in retail markets to reduce contamination with this pathogen.